Maintenance of habitable conditions within closed environments often requires carbon dioxide partial pressures to remain below about 0.5%. Carbon dioxide (CO.sub.2) is conventionally maintained at relatively low partial pressures via regenerable and nonregenerable CO.sub.2 sorbents, such as soda lime, molecular sieves, solid oxide sorbents, and others.
CO.sub.2 sorbents are prepared via paste extrusion or pelletization techniques, typically in the form of beads or pellets. Due to chemical and physical changes associated with absorption/desorption cycles of the sorbent, the life of these sorbents is limited. Cyclical operations cause volume changes in the sorbent which often result in pellet deterioration and breakage, known as "dusting". As the pellets deteriorate, the pressure drop across the sorbent bed increases, resulting in greater power requirements and a less efficient or effective sorbent bed.
Conventionally, the cyclical life of the solid CO.sub.2 sorbent has been increased by the addition of binders or by depositing the active ingredients of the sorbents onto inactive supports, such as porous ceramics or carbons. These binders and supports impart strength and provide high gas/solid contact areas. However, their use is undesirable in applications where the CO.sub.2 loading densities, in addition to weight, volume, and power considerations, are crucial factors. Since the binders and supports themselves are inactive, "dead" material, they merely consume volume and add weight. Therefore, in order to absorb a given amount of a substance, it is necessary to employ a greater amount of supported or bound sorbent than unsupported/unbound sorbent.
What is needed in the art is an unsupported sorbent having high loading densities, high CO.sub.2 sorption rates, and extended cyclical life.